Seasonal Climate Outlook Message for September to December 2003

The bottom line

SOI Remains Near Zero (Dated 17th September)

A neutral sea temperature pattern can be still found in the central Pacific Ocean. Overall, sea-surface temperatures remain close to average across most of the equatorial Pacific (temperature anomalies of -1 to +1oC) with no strong signals towards the development of either an El Nino or a La Nina.

The latest sea surface temperature map available at www.longpaddock.qld.gov.au highlights this neutral pattern.

Ocean and coupled ocean/atmosphere forecast models (GCM's) give an indication as to likely sea surface temperature development out to 9 months. Of 12 models that forecast out to January 2004, 11 indicate the development of a neutral sea temperature pattern and 1 indicates the potential development of an El Nino (or warm) sea temperature pattern.

Of the 8 models that forecast out to April 2004, all of them indicate the development of a neutral sea temperature pattern. While it is positive news that these models show the development of a neutral SST pattern (rather than the El Nino SST pattern) given current conditions our policy remains to recommend a cautious approach when considering the longer term outlook.

Try www.bom.gov.au/climate/ahead/ENSO-summary.shtml for more details.

Many readers of this column like to follow the timing of the MJO (also know as the 40day wave). The MJO is simply a band of low atmospheric pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 50 days.

While it is a tropical phenomenon, it appears to indicate the timing of potential rainfall events (but unfortunately not rainfall amounts) over central and southern Queensland.

The next passage of the MJO is expected to influence our weather in early October.

In the mean time for September to November there is a 30 to 50% probability of getting above the long term median rainfall for northern, central and western Queensland. For the south east quarter of the state, the probability of getting above the long-term median rainfall for the same period is marginally higher at 50-60%.

The current outlook is a slight improvement on this time last year. Based on these probabilities though, this forecast would not normally be regarded as indicating a high chance of getting the much needed well above average state wide 'drought-breaking' rain. It is worth remembering that September is also normally one of the drier months of the year.

For example, the long term September median rainfall level for Dalby is 32mm, Talwood is 24mm, Quilpie is 5mm, Birdsville is 1mm, Emerald is 10mm, Townsville is 3mm, Mareeba is 2mm, Cloncurry is 1mm, and Normanton and Weipa is 0mm.

The 30day average of the SOI as of the 17th September is plus 1.3. For increased confidence in seasonal conditions improving in the longer term (through to summer) the SOI needs to return to more positive monthly values.